Field effect transistors (FETs) made of III-N materials such as GaN exhibit desirable properties for power switches, such as high bandgaps and high thermal conductivity compared to silicon FETs. However, enhancement mode GaN FETs with semiconductor gates are undesirably susceptible to excessive gate leakage current when the gates are overbiased. Similarly, enhancement mode GaN FETs with insulated gates are susceptible to gate dielectric breakdown when the gates are overbiased.